In the production of optical fibers, a glass rod or preform, which is especially made to manufacture optical fibers, is processed in an optical fiber drawing system. The optical fiber drawing system generally comprises a furnace, a heat exchanger, a coating applicator, a dryer or curing furnace and a spool as shown by European Patent Application No. 0,079,188. Initially, the glass rod or preform is melted in the furnace to produce a small semi-liquid fiber. The semi-liquid fiber is then cooled and solidified as it falls through the air and through the heat exchanger. The cooled and solidified fiber from the heat exchanger is coated in the coating applicator, dried in the curing furnace or dryer and drawn with the spool.
The drawing rate of the optical fiber is dependent on the cooling rate of the optical fiber in the heat exchanger. That is, the rate at which the fiber can be withdrawn can be increased as the rate of cooling increases. To increase the rate of cooling, a coolant gas, such as helium or nitrogen, is normally introduced into the heat exchanger to directly cool the semi-liquid fiber by direct heat exchange. The direct heat exchange is made possible by designing the heat exchanger to provide a passageway or cylindrical hole running from the top to the bottom for passing the optical fiber, an inlet for introducing the coolant into the passageway or cylindrical hole and optionally at least one outlet for removing the coolant from the passageway or cylindrical hole. The flow of the coolant into the heat exchanger is usually controlled with metering valves and flow meters.
Although the drawing rate of the optical fiber is increased through employing the above heat exchanger, the coolant utilized is normally lost to the atmosphere through one or both ends of the passageway or cylindrical hole and/or the outlet, and is also contaminated with impurities, e.g., when air impurities infiltrate into the passageway or cylindrical hole where the coolant is located. Replacing this lost coolant gas represents a substantial cost to the optical fiber manufacturing process. Thus, there is a need for an effective and efficient coolant recovery system and heat exchanger, which could reduce the coolant losses and reduce the contamination of the coolant.